Phenol containing waste water of different concentrations occur in the synthesis of phenol, in coke oven plants and gas making plants, in lignite carbonization and, not of least importance, in the production of phenolformaldehyde resins (phenoplasts).
The removal of toxic phenol without residue and also the removal of the likewise toxic formaldehyde from waste waters of the above-mentioned branches of industry, particularly for a subsequent biological clarification of such waste water is now as ever a very important problem which until now has not been able to be solved satisfactorily within a large range of concentration.
In the mentioned phenoplasts for example in the so-called "reaction waters" which according to the condensation process can react either alkaline or acid, there can be present a content of volatile phenol in the range of 1,700 to 15,000 mg/l and of free formaldehyde between 1,200 and 8,000 mg/l (F. Meinck, H. Stoff, H. Kohlschutter, "Industrie-Abwasser," 4th edition, Gustav Fischer-Verlag, Stuttgart, 1968 page 619).
There are already a large number of processes for the purification of phenol containing waste water which, however, are not universally usuable over a large range of concentrations.
At high phenol concentrations, for example, for the purpose of recovery of phenol, a steam distillation can be suitable. Besides, there is a series of extraction processes in which an extraction of the phenol is undertaken with the help of, for example, benzene, toluene or tricresyl phosphate. Attendant on this process is the disadvantage that certain residual parts of the extraction agent enter the waste water; besides, the so-called "Degree of Washing" of the various processes is different so that it is not possible to remove the phenol without residue.
A total removal of phenol can be produced by evaporation of the waste water and burning of the residue. However, this process requires a high expenditure of energy.
At low phenol concentrations it is possible to remove a sufficient amount of phenol also with help of special activated carbon, but the effect depends on the amount of carbon, type and granulation as well as the process (duration of the action, pH and temperature of the waste water).
According to the composition and concentration of the phenol containing waste water the effect of the adsorption is very different and at average and high concentrations too expensive, e.g., from 1,000 ppm and higher.
A further adsorption process consists of the use of specific synthetic resins, e.g., polymethacrylates or polyvinyl benzenes. Thus, the phenol content in a phenol containing waste water can be reduced from 6,700 ppm to about 0.1 ppm (Albright U.S. Pat. No. 3,663,467 and Gustafson U.S. Pat. No. 3,531,463).
However, this type of adsorption process cannot be used in phenol-formaldehyde containing waste waters of the synthetic resin industry because in the thus treated waste water just as before the toxic formaldehyde remains behind.
Sporadically the phenol rich waste water can also be treated biologically according to the "Nocardia Process". Pure cultures such as organisms closely related to actinomyces are colonized in trickling filters or activated sludge plants.
In favorable cases a purification effect of 99% can be produced so that even with biological breakdown there always remains a certain residual amount.
The effect depends on the remaining conditions, thus the flora is severely injured by a too great amount of phenol or by other waste water poisons and eventually even destroyed.
The process therefore produces no guarantee for waste water detoxification.
Besides, for adopting such a special biological turf or activated sludge there must be added N and P containing nutrient salts (Gesundh. Ing. Vol. 81 (1960) pages 205 et seq.). This procedure requires the relatively expensive operation of a special biological clarification plant.
A well known process is the oxidation of phenol by means of chlorine dioxide. Chlorine dioxide is obtained either through the action of acids on chlorites, preferably sodium chlorite, or also by reaction of chlorine with sodium chlorite in, e.g., sulfuric acid medium.
However, in the last process there is the danger of chlorination of the phenol to the still more toxic chlorophenols. Besides, the oxidation does not go one hundred percent. This is true even for the development of chlorine dioxide by the action of acids on chlorites. Here also a substantial oxidation can be produced. However, our experiments of this type show, as can be seen from gas chromatographic analysis of this type of treated waste water, that after the oxidation there was always still present a greatly varying residual content of phenol in order of between more than 10 to above 100 ppm. Besides, these occurs in the gas chromatogram foreign peaks which have not been previously identified, from which it can be assumed that it is a matter of intermediate oxidation products (quinones, hydroquinones or eventually even chlorinated products) (see also H. Thieleman, Gesundh. Ing. Vol. 92 (1971) No. 10 page 297).
Also, there should not be disregarded the corrosion problems which occur in the strong acidification of the waste water.
According to data in the literature (Klossowski, Jerzy, Gaz, Woda Tech. Sanit. (1968) Vol. 42 pages 197-200) phenol and its derivatives are decomposed only in an amount of 83% by gaseous chlorine dioxide which is developed from sodium chlorite and sulfuric acid.
The oxidation of phenol by chlorine dioxide in the acid or neutral range should lead to p-benzoquinone as the end product of the phenol oxidation, while in alkaline medium by a high excess of chlorine dioxide (5 mg ClO.sub.2 to 1 mg phenol) there is formed a mixture of organic acids, chiefly maleic and oxalic acids (Chemical Abstracts, Vol. 79, 23266 m).
In Russian Patent 141,814 there is described the purification of waste waters of phenol-formaldehyde resin production wherein formaldehyde is removed by treatment of the water with quicklime at room temperature or at 98.degree. C. and phenol is removed by oxidation either electrochemically or with MnO.sub.2. This process is relatively expensive. By quicklime is meant calcium hydroxide.
In another process the waste water purification from phenol, methanol and formaldehyde is undertaken by means of a so-called "Liquid Phase Oxidation" (I. S. Stepanyan, I. A. Vinokur, G. M. Padaryan, khim. prom (1972) Vol. 6 pages 30-31 or Int. Chem. Eng. Vol. 12 (1972) No. 4 pages 649-651). In this process, the waste water is nozzled into an electrically heated reactor by means of air under 40 bar pressure and at 200.degree. C. However, test data have only given a degree of oxidation around 95% for phenol, 77% for methanol and 93% for formaldehyde.
In another series of experiments, the degree of oxidation is only 80% for the named substances. The process is industrially very expensive. There remains a residual amount of the toxic acting materials.
In German OS No. 2,404,264 there is described a process for the preliminary purification of waste water from phenol, formaldehyde and their reaction products after which there is added to the waste water soluble aminoplast resin precondensates or their aqueous solutions. The reaction mixture is held at the boiling temperature in the alkaline range for 2 to 8 hours, subsequently neutralized and the precipitated reaction product separated.
As can be seen from the examples with this process there can merely be produced a preliminary purification of such waste water; a complete removal of phenol and formaldehyde is impossible.
To be sure chlorine dioxide is preferred for industrial processes as the oxidation agent. Only it cannot be produced according to the previously described processes since then the oxidation does not proceed completely.
However, on the other hand, chlorine dioxide must be produced just before its use for safety reasons, because it cannot be stored as a supply. The direction production of chlorine dioxide according to the processes mentioned, however, cannot be adjusted to the particular demand. In production of chlorine dioxide in a so-called "Chlorine Dioxide Plant" there is not excluded the possibility of the formation of a strong excess of chlorine dioxide. This means an inadmissibly high loading of the waste water with the chlorine dioxide likewise strongly toxic to the activated sludge. Besides, here also the oxidation does not proceed completely.
The object of the invention, therefore, is the complete elimination of phenol from waste water in an industrially simple manner.